CN111326723B - Silicon-carbon composite negative electrode material for lithium ion battery and preparation method thereof - Google Patents

Silicon-carbon composite negative electrode material for lithium ion battery and preparation method thereof Download PDF

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CN111326723B
CN111326723B CN202010119379.3A CN202010119379A CN111326723B CN 111326723 B CN111326723 B CN 111326723B CN 202010119379 A CN202010119379 A CN 202010119379A CN 111326723 B CN111326723 B CN 111326723B
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silicon powder
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CN111326723A (en
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王兴蔚
侯佼
侯春平
贺超
杨丹
马少宁
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Bolt New Materials Yinchuan Co ltd
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Abstract

The invention discloses a silicon-carbon composite negative electrode material for a lithium ion battery and a preparation method thereof, and aims to solve the technical problems of improving the electrochemical performance and safety of the silicon-carbon composite negative electrode material and reducing the cost. The silicon-carbon composite negative electrode material for the lithium ion battery is of a core-shell structure; the core consists of long-strip flaky nano silicon powder and micro graphite, amorphous carbon coated on the surfaces of the nano silicon powder and the micro graphite and amorphous carbon bridged around the coated nano silicon powder and micro graphite, and micro pores are distributed in the amorphous carbon and on the surface of the amorphous carbon; the shell is a carbon coating layer coated on the surface of the core. The preparation method comprises the steps of silicon mud coarse powder, acid washing, nanocrystallization, ultrasonic dispersion, spray granulation, high-temperature fusion and coating and high-temperature calcination. Compared with the prior art, the invention has the characteristics of high capacity, high-rate charge and discharge performance, long cycle life, safety, excellent processing performance, low production cost, easy control and suitability for large-scale industrial production.

Description

Silicon-carbon composite negative electrode material for lithium ion battery and preparation method thereof
Technical Field
The invention relates to a negative electrode material for a lithium ion battery and a preparation method thereof, in particular to a silicon-carbon composite negative electrode material and a preparation method thereof.
Background
At present, a commercial lithium ion battery (battery) mainly adopts a graphite carbon material as a negative electrode active material, but the specific capacity of the carbon material is lower, the theoretical capacity is 372mAh/g, and the energy density of a battery system formed by the carbon material and a lithium iron phosphate, lithium manganate or nickel cobalt lithium manganate positive electrode material is generally 150 Wh/Kg; meanwhile, the lithium intercalation potential of graphite is close to the lithium deposition potential, and lithium is easy to separate out during low-temperature charging or high-rate charging and discharging, so that the safety problem is caused. Therefore, the conventional carbon-based negative electrode material has difficulty in meeting the development requirements of miniaturization of electronic equipment and high power and high capacity of lithium ion batteries for power, and further research and development of a novel negative electrode material for the lithium ion batteries with high energy density, high safety performance and long cycle life performance are needed.
The theoretical lithium storage capacity of silicon is up to 4200mAh/g, and the silicon is a high-specific-capacity negative electrode material with the most development potential and becomes a research hotspot in the field of lithium ion battery materials. However, the silicon is singly used as a negative electrode material, and the battery is easy to generate electrode cracking and active substance particle pulverization due to large volume expansion change in the charging and discharging processes, so that the electrode capacity is rapidly attenuated; meanwhile, the electron conductivity of silicon is poor, which is not favorable for the exertion of the capacity and rate capability of the active ingredients of the electrode. Aiming at the defects of the silicon material, the modification method mainly comprises the steps of nano-modification and compounding. The nano silicon-based material with special appearance and structure such as silicon nanoparticles, silicon nanowires, silicon nanotubes and silicon-based nano films is prepared, so that the volume change of the cathode active material is more uniform, the cathode material can obtain enough space to relieve the volume change of silicon, but the nano material is easy to agglomerate, a new volume effect can be generated in the circulation process, the problem of the cycling stability of the silicon material cannot be fundamentally solved by single nano treatment, and the nano silicon material with special structure and appearance has high preparation cost and complex process and is not beneficial to industrial popularization; the composite material introduces an active or inactive buffer matrix with good conductivity and small volume effect on the basis of reducing the volume effect of a silicon active phase through nanocrystallization, and improves the cycle stability of the silicon-based negative electrode material by adopting a volume compensation and conductivity increasing mode. The silicon-carbon composite material is a silicon-based material which is most expected to realize large-scale industrialization, but the problems of high cost, complex process, high control difficulty and poor batch stability of the nano silicon powder are urgently needed to be solved.
The fact that fossil energy such as petroleum and coal is in short supply and environmental pollution is not competitive, which brings infinite development space for new energy and renewable energy products and methods. The photovoltaic power generation is widely popularized and applied as a novel clean energy for effectively solving the haze weather, the installed capacity of the photovoltaic power generation is sharply increased year by year, and the productivity of the main raw material silicon wafer of the crystalline silicon solar cell is greatly improved. In the slicing process of the silicon wafer, the loss of a kerf material is inevitable, so that high-purity silicon powder with nearly half quality, a cutting additive and other impurities are mixed together to form a large amount of cutting waste silicon mud. The mortar cutting method has the advantages that the silicon powder surface is seriously polluted and is difficult to separate from silicon carbide, green recovery and regeneration recycling of silicon mud are difficult to realize, the cutting process of the silicon wafer is simpler, cleaner and more environment-friendly than the traditional mortar cutting process along with the development and application of the diamond wire cutting method in crystalline silicon processing in two years, the purity of waste silicon powder in the silicon mud is greatly improved, the separation difficulty is greatly reduced, and the recovery and high-value utilization of the silicon mud are gradually possible. At present, the silicon mud is mainly used as a deoxidizer for steel smelting and alloy smelting, but the treatment process is complex, the energy consumption is high, the economic feasibility is poor, and the large-area popularization is not realized.
Therefore, chinese patent publication No. CN107732200A discloses a method for preparing a negative electrode material of a lithium ion battery from photovoltaic industrial waste, which comprises pretreating the photovoltaic industrial waste to obtain silicon powder, preparing the negative electrode material of the lithium ion battery, and treating the photovoltaic industrial waste to modify the silicon raw material, thereby promoting the commercial application of the silicon negative electrode. However, the particle size of the obtained silicon powder is 300-500 nm, the large particle size of the powder can cause the silicon material to have a significant volume effect in the charging and discharging process, and is not beneficial to the exertion of the cycle performance of the silicon-carbon composite cathode material, and the first coulombic efficiency of the silicon-carbon material prepared by the method is less than 70%, so that the silicon-carbon material is difficult to be applied in actual industrial production.
Chinese patent publication No. CN109037665A discloses a method for preparing a nano-silicon negative electrode material by using waste silicon slag in photovoltaic industry, which comprises the steps of crushing to obtain waste silicon powder, and performing secondary purification, coarse powder and fine powder treatment and spray drying to obtain the nano-silicon negative electrode material. However, the repeated physical crushing mode is adopted for multiple times in the preparation process, the efficiency is low, the nano-grade silicon material is directly dried and treated by using the spray drying mode, the yield of the silicon powder is low, the loss is large, the grinding aid in the fine powder treatment process is difficult to completely pyrolyze and volatilize at the spray drying temperature of 80-150 ℃, and the newly introduced impurities influence the electrochemical performance and the safety of the final cathode material.
Disclosure of Invention
The invention aims to provide a silicon-carbon composite negative electrode material for a lithium ion battery and a preparation method thereof, and aims to solve the technical problems of improving the electrochemical performance and safety of the silicon-carbon composite negative electrode material and reducing the cost.
The invention adopts the following technical scheme: a silicon-carbon composite negative electrode material for a lithium ion battery is of a core-shell structure; the core is composed of long-strip flaky nano silicon powder and micropowder graphite, amorphous carbon coated on the surfaces of the nano silicon powder and micropowder graphite and amorphous carbon bridged around the coated nano silicon powder and micropowder graphite, micro pores are distributed in the amorphous carbon and on the surface of the amorphous carbon, the amorphous carbon is formed by carbonizing an adhesive at a high temperature of 650-1100 ℃, and the mass ratio of the nano silicon powder to the micropowder graphite to the carbonizing adhesive is 4-15: 100: 5.0 to 20.0; the shell is a carbon coating layer coated on the surface of the core, and the mass of the coating layer is 5-15% of that of the core.
The nano silicon powder and the micro graphite powder are randomly and uniformly distributed.
The length dimension of the nano silicon powder is 400-800 nm, and the width and thickness dimensions are 50-100 nm; the average particle size D50 of the micro powder graphite is 2-10 μm.
The amorphous carbon is formed by carbonizing a nonionic surfactant at a high temperature of 650-1100 ℃.
A preparation method of a silicon-carbon composite negative electrode material for a lithium ion battery comprises the following steps:
coarse powder of silicon mud
Crushing the silicon sludge to obtain silicon powder with the particle size of below 2 mu m;
second, acid cleaning
Stirring and soaking silicon powder in acid liquor with the concentration of 0.5-3 mol/L, wherein the mass of the silicon powder is 25-70% of that of the acid liquor, the stirring and soaking speed is 150-500 r/min, the stirring and soaking time is 0.5-5 h, after the stirring and soaking is finished, washing to be neutral, performing suction filtration, centrifugal dehydration and drying, and the mass content of water is lower than 0.2%, so as to obtain acid-washed silicon powder;
three, nano treatment
Taking a nonionic surfactant as a grinding aid, grinding and grinding the zirconium oxide balls with the diameter of 0.05-0.1 mm, and carrying out wet grinding nanocrystallization treatment on the acid-washed silicon powder in a protective gas atmosphere, wherein the mass ratio of the acid-washed silicon powder to the grinding aid to the zirconium oxide balls is 85-95: 15-5: 300, taking the acid-washed silicon powder, the mixed liquid of the grinding aid and the solvent as grinding slurry, wherein the acid-washed silicon powder accounts for 25-45% of the mass fraction of the grinding slurry, and separating zirconia balls after nano treatment to obtain nano silica sol slurry, wherein the length of the nano silica is 400-800 nm, and the width and thickness of the nano silica are 50-100 nm;
fourthly, ultrasonic dispersion
According to the mass ratio of the micro-powder graphite to the carbonizable binder of 100: 5.0 to 20.0, carrying out ultrasonic pre-dispersion on the micro-powder graphite and the carbonizable binder in a solvent at the rotating speed of 150 to 600r/min, the frequency of 10 to 20kHz and the power density of 0.25 to 0.45w/cm2After the ultrasonic pre-dispersion time is 30-90 min, adding the nano silica sol slurry, and performing ultrasonic mixing dispersion at the rotating speed of 150-600 r/min, the frequency of 10-20 kHz and the power density of 0.25-0.45 w/cm2And (3) performing ultrasonic mixing and dispersing for 40-120 min to obtain mixed slurry with the solid content of 20-35%, wherein the mass ratio of the nano silicon powder to the micro graphite powder is 4-15: 100, respectively;
spray granulation
Carrying out spray drying granulation on the mixed slurry, wherein the inlet temperature of the spray drying granulation is 150-250 ℃, and the outlet temperature of the spray drying granulation is 50-110 ℃, so as to obtain a secondary particle precursor;
sixthly, high-temperature fusion and coating
Stirring the secondary particle precursor at a stirring speed of 15-30 r/min under a protective gas atmosphere, heating to 300-450 ℃ at a heating speed of 2-5 ℃/min, preserving heat for 60-180 min, starting heat preservation, atomizing the liquid coating agent at room temperature according to the mass of the solid content of the liquid coating agent being 9-25% of that of the secondary particle precursor, and spraying the atomized liquid coating agent onto the surface of the secondary particle precursor in a reaction kettle; after the heat preservation is finished, heating to 650-850 ℃ in a second heat preservation area at a stirring speed of 25-60 r/min and a temperature rise speed of 2-5 ℃/min, preserving the heat for 60-240 min, naturally cooling to room temperature, and stirring to obtain a silicon-carbon composite anode material precursor;
seven, high temperature calcination
And heating the precursor of the silicon-carbon composite negative electrode material to the calcining temperature of 900-1100 ℃ at the heating rate of 3-5 ℃/min under the protective gas atmosphere, calcining for 0.5-3.0 h, and naturally cooling to the room temperature after the calcining is finished to obtain the silicon-carbon composite negative electrode material for the lithium ion battery.
The secondary acid solution in the steps of the method is more than one of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, carbonic acid, acetic acid and oxalic acid solution.
Method step three of the invention said nonionic watchThe surfactant is more than one of polyethylene glycol, polyvinylpyrrolidone, fatty alcohol-polyoxyethylene ether, alkylphenol ethoxylate, polyoxyethylene alkylamide, fatty acid-polyoxyethylene ester and polyoxyethylene alkylammonium; the wet grinding slurry is prepared from more than one of ethanol, propanol, acetone, isopropanol, N-hexane and N-methylpyrrolidone as solvent, the protective gas is nitrogen, helium, neon, argon, krypton or xenon, and the flow rate is 0.2-1.0 m3/h。
The method comprises the following steps that step four, micro powder graphite is a small-particle-size tailing in the production process of the lithium ion battery negative electrode material, the average particle size D50 is 2-10 mu m, the micro powder graphite comprises more than one of graphitized mesophase carbon microspheres, petroleum coke, pitch coke, needle coke and natural graphite, the carbon content is more than 99.95%, and the carbonizable binder is more than one of modified alkyd resin, furan resin, phenolic resin, polyvinyl alcohol, polyacrylonitrile and styrene butadiene rubber; the solvent is more than one of deionized water, methanol, ethanol, propanol, isopropanol, tetrahydrofuran and ethyl acetate.
The liquid coating agent in the sixth step of the method is more than one of emulsified asphalt, water-soluble phenolic resin solution, polyglycol ether and diethyl phthalate; the atomization rotating speed is 8000-20000 r/min; the protective gas is nitrogen, helium, neon, argon, krypton or xenon, and the flow rate is 0.2-1.0 m3/h。
The method comprises the step seven of using nitrogen, helium, neon, argon, krypton or xenon as protective gas with the flow of 0.4-1.2 m3/h。
Compared with the prior art, the silicon-carbon composite negative electrode material for the lithium ion battery has the characteristics of high capacity, high-rate charge and discharge performance, long cycle life, safety, excellent processing performance, environmental friendliness, low production cost, easiness in control and suitability for large-scale industrial production.
Drawings
Fig. 1 is an X-ray diffraction spectrum of a silicon-carbon composite anode material for a lithium ion battery of example 3.
FIG. 2 is a SEM photograph of the silicon powder after acid washing in example 3.
Fig. 3 is an SEM photograph of the silicon-carbon composite anode material for lithium ion battery of example 3.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The silicon-carbon composite negative electrode material (negative electrode material) for the lithium ion battery is of a core-shell structure.
The core in the core-shell structure is composed of long and flaky nano silicon powder and micro graphite which are distributed in a disordered manner, amorphous carbon coated on the surfaces of the nano silicon powder and the micro graphite, and amorphous carbon bridged around the coated nano silicon powder and the micro graphite, and micro pores (micropores) are randomly distributed in the amorphous carbon and on the surface of the amorphous carbon. The secondary particles are composed of nano silicon powder, micro graphite powder and amorphous carbon which is coated on the surfaces of the nano silicon powder and the micro graphite powder and has a micro pore (micropore) structure and is bridged around the coated nano silicon powder and the coated micro graphite powder.
Wherein, the disordered distribution is that the nano silicon powder and the micro graphite are irregularly and uniformly distributed. The length dimension of the long-strip flaky nano silicon powder is 400-800 nm, and the width and thickness dimensions are 50-100 nm. The average particle diameter D50 of the fine graphite powder is 2-10 μm. The amorphous carbon is formed by carbonizing a non-ionic surfactant and a carbonizable binder at a high temperature of 650-1100 ℃. The bridge is formed by combining the amorphous carbon with the surfaces of the coated nano silicon powder and the micro graphite by chemical bonds. The mass ratio of the nano silicon powder to the micro graphite to the carbonizable binder is 4-15: 100: 5.0 to 20.0.
The shell (coating layer) in the core-shell structure is a uniform and compact carbon coating layer coated on the surface of the core, and the mass of the coating layer is 5-15% of that of the core. The carbon coating layer is formed by carbonizing the liquid coating agent at a high temperature of 900-1100 ℃.
During the charge and discharge of the lithium ion battery, lithium ions are embedded and embedded in the negative electrode material nano silicon powder in the process of high-rate charge and discharge, and the silicon has poor conductivity, so that the nano silicon powder with a long strip-shaped lamellar structure can pass through in the direction with a small geometric dimension and a short diffusion path, the nano silicon powder and micro powder graphite are in disordered distribution in secondary particles, the macroscopic expression of nuclear particles is isotropic, the stability of the negative electrode material structure can be effectively improved, and the lithium ion battery is suitable for embedding and embedding in the high-rate charge and discharge process. The amorphous carbon intermediate layer formed by carbonizing the nonionic surfactant and the carbonizable binder in the secondary particles has good compatibility with electrolyte, a compact and stable-structure solid electrolyte interface SEI film can be formed on the interface, organic solvent molecules can be effectively prevented from being inserted into a nuclear micropowder graphite sheet layer of the negative electrode material, and the cycle stability of the negative electrode material is improved. The micro pores randomly distributed in the amorphous carbon intermediate layer and on the surface can reserve space for the charge-discharge expansion of the nano silicon powder, and absorb and eliminate the stress change of the negative electrode material in the charge-discharge process.
The surface of the negative electrode material is coated with the uniform and compact carbon coating layer, so that the mechanical strength of the negative electrode material is effectively improved, the carbon coating layer and the core form a core-shell structure with hard outside and soft inside, the volume effect of the negative electrode material in the high-rate charge and discharge process can be greatly buffered, a good microporous lithium storage mechanism and excellent liquid absorption performance are realized, and the charge and discharge specific capacity, the rate charge and discharge performance and the low-temperature performance of the negative electrode material are effectively improved.
The preparation method of the silicon-carbon composite negative electrode material for the lithium ion battery comprises the steps of taking silicon mud obtained after monocrystalline silicon or polycrystalline silicon is cut by diamond wires as a silicon source, taking micro-powder graphite tailings with the average particle size D50 of 2-10 mu m in the production process of the carbon negative electrode material for the lithium ion battery as a carbon source, uniformly mixing and dispersing the silicon mud with micro-powder graphite after coarse powder, acid washing and nanocrystallization treatment, and carrying out spray granulation, high-temperature fusion and coating and high-temperature calcination under the action of a non-ionic surfactant and a carbonizable binder organic substance to obtain the silicon-carbon composite negative electrode material for the lithium ion battery with a core-shell structure with high tap density and good appearance. The method comprises the following steps:
coarse powder of silicon mud
Coarse powder treatment is carried out on the silicon mud at room temperature (20 ℃), and the agglomerated silicon mud is crushed to the particle size of below 2 mu m to obtain the silicon powder.
The silicon mud is waste material obtained after monocrystalline silicon or polycrystalline silicon is cut by diamond wires, the moisture content is lower than 0.2%, silicon powder particles in the silicon mud are in a strip slice shape, the length dimension is 800-1500 nm, the width and thickness dimensions are 50-100 nm, and the surface of the silicon mud is coated with a passivation film formed by organic polymers in diamond wire cutting liquid.
The pulverization adopts the mechanical pulverization, the air flow pulverization or the grinding pulverization of the prior art. The crushing equipment adopts a universal crusher, a mechanical crusher, a jet mill, an ultrafine crusher or a ball mill crusher in the prior art.
The silicon mud coarse powder has the function of crushing and dispersing the agglomerated silicon mud into silicon powder, and the acid washing efficiency and the function of the acid washing step are improved.
Second, acid cleaning
Stirring and soaking silicon powder in acid liquor with the concentration of 0.5-3 mol/L, wherein the mass of the silicon powder is 25-70% of that of the acid liquor, the stirring and soaking speed is 150-500 r/min, the stirring and soaking time is 0.5-5 h, washing the silicon powder to be neutral by deionized water after the stirring and soaking are finished, performing suction filtration, centrifugal dehydration and drying according to the prior art, and obtaining the acid-washed silicon powder, wherein the mass content of water is lower than 0.2%.
The acid solution is one or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, carbonic acid, acetic acid and oxalic acid solution.
The acid wash serves to remove metallic impurities, compounds and organic polymers from the silica sludge.
Three, nano treatment
Taking a nonionic surfactant as a grinding aid, grinding and grinding the zirconium oxide balls with the diameter of 0.05-0.1 mm, and carrying out wet grinding nanocrystallization treatment on the acid-washed silicon powder in a protective gas atmosphere, wherein the mass ratio of the acid-washed silicon powder to the grinding aid to the zirconium oxide balls is 85-95: 15-5: 300, taking the acid-washed silicon powder, the mixed liquid of the grinding aid and the solvent as grinding slurry, taking the acid-washed silicon powder as 25-45% of the mass fraction of the grinding slurry, separating zirconia balls after nano treatment to obtain nano silica sol slurry, wherein the length dimension of the nano silicon is 400-800 nm, and the width and thickness dimensions are 50-100 nm.
The solvent of the wet grinding slurry is more than one of ethanol, propanol, acetone, isopropanol, N-hexane and N-methylpyrrolidone.
The nonionic surfactant is one or more of polyethylene glycol, polyvinylpyrrolidone, fatty alcohol-polyoxyethylene ether, alkylphenol ethoxylate, polyoxyethylene alkylamide, fatty acid-polyoxyethylene ester and polyoxyethylene alkylammonium.
The protective gas is nitrogen, helium, neon, argon, krypton or xenon, and the flow rate is 0.2-1.0 m3/h。
The nanocrystallization treatment adopts a rod pin type nanometer sand mill or a high-energy nanometer ball mill in the prior art.
The nano treatment has the effects of preparing the nano silicon powder with the strip-shaped sheet structure, the length dimension of which is 400-800 nm, and the width dimension and the thickness dimension of which are 50-100 nm, in the preparation process of the nano silicon powder, the nonionic surfactant serves as a grinding aid on one hand to effectively improve the nano efficiency of the silicon powder, and serves as a stabilizer on the other hand to prevent the nano silicon powder from agglomerating and settling, so that the grinding slurry finally forms a stable nano silica sol system.
Fourthly, ultrasonic dispersion
At room temperature (20 ℃), mixing the micro-powder graphite and the carbonizable binder in a mass ratio of 100: 5.0 to 20.0, carrying out ultrasonic pre-dispersion on the micro-powder graphite and the carbonizable binder in a solvent at the rotating speed of 150 to 600r/min, the frequency of 10 to 20kHz and the power density of 0.25 to 0.45w/cm2The ultrasonic pre-dispersion time is 30-90 min, the nano silica sol slurry is added after the pre-dispersion is uniform, and the ultrasonic mixing dispersion is carried out at the rotating speed of 150-600 r/min, the frequency of 10-20 kHz and the power density of 0.25-0.45 w/cm2And (3) ultrasonic mixing and dispersing for 40-120 min, and uniformly mixing to obtain mixed slurry with the solid content of 20-35%, wherein the mass ratio of the nano silicon powder to the micro graphite is 4-15: 100.
the micro-powder graphite is a small-particle-size tailing material in the production process of the lithium ion battery negative electrode material, the average particle size D50 is 2-10 mu m, the micro-powder graphite comprises more than one of graphitized mesocarbon microbeads, petroleum coke, pitch coke, needle coke and natural graphite, and the carbon content is more than 99.95%.
The carbonizable binder is more than one of modified alkyd resin, furan resin, phenolic resin, polyvinyl alcohol, polyacrylonitrile and styrene butadiene rubber.
The solvent is more than one of deionized water, methanol, ethanol, propanol, isopropanol, tetrahydrofuran and ethyl acetate.
The nano silica sol slurry, the micro powder graphite and the carbonizable binder are subjected to liquid phase ultrasonic dispersion, so that the dispersion uniformity of solute materials of the mixed slurry can be effectively improved, the nano silica powder and the micro powder graphite are randomly and uniformly distributed, and the stability of a secondary particle structure prepared by subsequent spray granulation and the consistency of components of a negative electrode material are ensured. In the ultrasonic pre-dispersion and ultrasonic mixing dispersion processes, ultrasonic and rotating speed are adopted simultaneously, so that the mixing dispersion efficiency is improved, and the slurry is prevented from being layered.
Spray granulation
And carrying out spray drying granulation on the mixed slurry, wherein the inlet temperature of the spray drying granulation is 150-250 ℃, and the outlet temperature of the spray drying granulation is 50-110 ℃, so as to obtain a secondary particle precursor. The average particle diameter D50 of the secondary particle precursor is 10-18 μm.
In the spray drying granulation process, the passivation film on the surface of the silicon powder can effectively prevent the surface oxidation of the silicon powder at high temperature. The passivation film is an organic film layer with good thermal stability formed by depositing organic polymers in cutting liquid on the surface of the effective components of silicon mud in the process of cutting a silicon wafer by a diamond wire.
Sixthly, high-temperature fusion and coating
Putting the secondary particle precursor into a high-temperature reaction kettle, under the protective gas atmosphere, stirring at a speed of 15-30 r/min, heating from room temperature to a first temperature preservation area of 300-450 ℃ for the first time at a heating rate of 2-5 ℃/min, keeping the stirring speed, preserving the temperature for 60-180 min, starting the heat preservation, atomizing the liquid coating agent to the surface of the secondary particle precursor in the reaction kettle by using an electric spraying centrifugal atomizer according to the solid content mass of the liquid coating agent of 9-25% of that of the secondary particle precursor, wherein the rotating speed of the atomizer is 8000-20000 r/min, and the spraying temperature of the liquid coating agent is room temperature; and after the heat preservation is finished, heating to 650-850 ℃ of a second heat preservation area at a temperature rise speed of 2-5 ℃/min according to a stirring speed of 25-60 r/min, keeping the stirring speed, preserving the heat for 60-240 min, naturally cooling the high-temperature reaction kettle to room temperature, and stirring to obtain the silicon-carbon composite anode material precursor.
The liquid coating agent is more than one of emulsified asphalt, water-soluble phenolic resin solution, polyglycol ether and diethyl phthalate.
The protective gas is nitrogen, helium, neon, argon, krypton or xenon, and the flow rate is 0.2-1.0 m3/h。
The stirring mode of the high-temperature reaction kettle is horizontal stirring and vertical stirring.
The porosity of the precursor of the secondary particles after spray granulation is generally higher, and the components have larger defects of holes and pores, and the mixture is heated, kept warm and stirred for the first time for fusion, can fully soften and melt the nonionic surfactant and the carbonizable binder in the secondary particle precursor base material, continuously infiltrating and repairing the defects of the holes and the pores in a liquid phase state, then performing heat treatment in a second heat preservation area and high-temperature calcination in the step seven to generate amorphous carbon, uniformly coating the amorphous carbon on the surfaces of the nano silicon powder and the micro graphite, and bridging the coated nano silicon powder and the micro graphite by chemical bonds, can effectively improve the compactness and structural stability of the secondary particles, improve the tap density of the cathode material, meanwhile, the residual micro pores which are not completely repaired by high-temperature fusion in the secondary particles are randomly distributed in and on the surface of the amorphous carbon formed by carbonization, so that the volume stress of the nano silicon powder in the charging and discharging process can be effectively relieved. The liquid coating agent is sprayed under the first heat preservation condition, because the temperature in the reaction kettle is low and the thermal field is stable, the coating agent can be in full time to be in dipping contact with the secondary particles in a homogeneous state, the carbon source coating agent can be uniformly and completely coated on the surfaces of the secondary particles in the second heating, heat preservation, stirring and fusion process, and a carbon coating layer with a uniform and compact structure is generated through the seven high-temperature calcination steps, so that the cathode material finally forms a core-shell structure with hard outside and soft inside, the stability and the processability of the cathode material structure are effectively improved, and the lithium ion is embedded and embedded out in the process of high-rate charge and discharge.
Seven, high temperature calcination
And (3) placing the silicon-carbon composite negative electrode material precursor in a high-temperature atmosphere furnace, heating to the calcining temperature of 900-1100 ℃ at the heating rate of 3-5 ℃/min under the protective gas atmosphere, calcining for 0.5-3.0 h, naturally cooling to the room temperature in the furnace after the calcining is finished, scattering and grading to obtain the silicon-carbon composite negative electrode material for the lithium ion battery.
The protective gas is nitrogen, helium, neon, argon, krypton or xenon, and the flow rate is 0.4-1.2 m3/h。
The negative electrode material prepared by the method is used for physical performance test of crops, and an XRD (X-ray diffraction) -7000X-ray diffractometer of Shimadzu corporation in Japan is used for determining an XRD map; observing the appearance of the negative electrode material by using a Zeiss GeminiSEM 500 field emission scanning electron microscope; testing the particle size of the negative electrode material by using a BT-9300ST laser particle size analyzer of Dandongbelter company; testing the tap density of the cathode material powder by using an Autotap type tap density instrument of the Congta company in America; the specific surface area of the negative electrode material was measured by a JW-DX type specific surface area tester from shin-gabo corporation.
The negative electrode material prepared by the method is used for chemical performance test, and the negative electrode materials of examples 1-6 and the silicon-carbon negative electrode material of the comparative example are used as negative electrode active substances for half-cell test. According to the mass ratio, the negative electrode active substance is conductive carbon black SP, sodium carboxymethylcellulose CMC and styrene butadiene rubber SBR (95: 2:1.5: 1.5), the solid content is 40%, the slurry is coated on a Cu film, the Cu film is dried for 12 hours at 70 ℃, rolled and stamped, a metal lithium sheet is used as a counter electrode, and fluoroethylene carbonate FEC: ethylene carbonate EC: ethyl methyl carbonate EMC ═ 1: 2: preparing electrolyte, and preparing a CR2032 button type experimental battery in a German Braun MBRAUN glove box protected by high-purity argon by using a polypropylene PP, polyethylene PE and polypropylene PP multilayer composite film (laminated structure) as a diaphragm. The method comprises the steps of testing the electrical performance of a button type experimental battery by using a CT2001A type blue electricity battery testing system of blue electricity electronic products Limited company in Wuhan City, wherein the charging and discharging voltage range is 0.003-2.0V, the first discharging capacity mAh/g and the first efficiency of 0.1C are measured, 1C charging and discharging cycle testing is carried out after 0.1C charging and discharging activation is carried out for 3 weeks, and the cycle capacity retention rate of 100 weeks is calculated by using the ratio of the 1C discharging capacity of 100 weeks to the 1C discharging capacity of 1 week.
Example 1
Firstly, crushing the silicon mud into silicon powder with the particle size of less than 2 microns by using a jet mill.
Secondly, adding the silicon powder into 0.5mol/L hydrochloric acid solution, wherein the adding amount is 25% of the mass of the acid solution, stirring and soaking for 5.0h at the rotating speed of 150r/min, and after pickling is finished, performing suction filtration, centrifugal dehydration and drying to obtain pickled silicon powder with the water mass content of less than 0.2%.
Thirdly, the nitrogen flow is 0.2m3Under the protection of a/h atmosphere, ethanol is used as a solvent, polyethylene glycol is used as a grinding aid, a mixed solution of acid-washed silicon powder, the grinding aid and the solvent is used as grinding slurry, a zirconia ball with the diameter of 0.05mm is used as a grinding medium, the acid-washed silicon powder accounts for 25% of the mass fraction of the grinding slurry, and the mass ratio of the acid-washed silicon powder to the grinding aid to the zirconia ball is 85: 15: and 300, carrying out wet grinding nanocrystallization treatment on the pickled silicon powder by using a pin-type nanometer sand mill, and separating zirconia balls after grinding to obtain nanometer silica sol slurry with the length dimension of 400-800 nm and the width and thickness dimensions of 50-100 nm.
Weighing 1000g of graphitized mesocarbon microbeads with carbon content of more than 99.95 percent and average particle size D50 of 2 mu m and 200g of modified alkyd resin, adding the graphitized mesocarbon microbeads and the modified alkyd resin into a methanol solution, wherein the rotating speed is 600r/min, the frequency is 20kHz, and the power density is 0.45w/cm2After 30min of ultrasonic pre-dispersion, 600g of nano silica sol slurry is added, and under the same rotating speed, frequency and power density, ultrasonic mixing and dispersion are carried out for 40min, so as to obtain mixed slurry with 20% of solid content.
And fifthly, carrying out spray granulation on the mixed slurry at the inlet temperature of 250 ℃ and the outlet temperature of 110 ℃ to obtain a secondary particle precursor with the average particle size D50 of 10 microns.
Sixthly, putting the secondary particle precursor into a high-temperature reaction kettle with the nitrogen flow of 0.2m3In the atmosphere of/h, the stirring speed is 15r/min, the temperature is increased from room temperature to 450 ℃ at the temperature increase speed of 2 ℃/min, the temperature is kept for 60min, the emulsified asphalt is sprayed to the surface of the secondary particle precursor in the reaction kettle by using a centrifugal spraying electric atomizer at room temperature according to the mass of the solid content of the emulsified asphalt being 25 percent of that of the secondary particle precursor, and the rotating speed of the atomizer is 8000 r/min; after the heat preservation is finished, stirring at the speed of stirringHeating to 850 ℃ at the temperature rise speed of 2 ℃/min at the rate of 25r/min, keeping the temperature for 60min, naturally cooling to room temperature in a high-temperature reaction kettle, and stirring to obtain the silicon-carbon composite anode material precursor.
Seventhly, placing the silicon-carbon composite anode material precursor in a high-temperature atmosphere furnace, wherein the flow of xenon is 0.4m3Heating to 900 ℃ at the heating rate of 3 ℃/min in the atmosphere of/h, calcining for 3.0h, naturally cooling to room temperature in the furnace after the calcining is finished, scattering and grading to obtain the silicon-carbon composite negative electrode material for the lithium ion battery.
The silicon-carbon composite negative electrode material for the lithium ion battery obtained in the embodiment 1 is sieved by a 200-mesh sieve, and then physical performance and chemical performance tests are carried out. The average particle diameter D50 of the negative electrode material was 10.5. mu.m, and the specific surface area was 1.87m2The tap density of the negative electrode material powder is 1.20g/cm3The first discharge capacity at 0.1C is 562.0mAh/g, the first efficiency is 91.3%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is not less than 84.2%, and the test results are summarized in Table 1.
Example 2
Firstly, the silicon mud is crushed into silicon powder with the particle size of less than 2 microns by a universal crusher.
Secondly, adding the silicon powder into 1.0mol/L nitric acid solution, wherein the adding amount is 35% of the mass of the acid solution, stirring and soaking for 3.5 hours at the rotating speed of 250r/min, and after pickling is finished, performing suction filtration, centrifugal dehydration and drying to obtain pickled silicon powder with the water mass content of less than 0.2%.
Third, the flow rate of the helium gas is 0.4m3Under the protection of a/h atmosphere, propanol is used as a solvent, polyvinylpyrrolidone is used as a grinding aid, a mixed solution of silicon powder, the grinding aid and the solvent after pickling is used as grinding slurry, a zirconia ball with the thickness of 0.05mm is used as a grinding medium, the silicon powder accounts for 30% of the mass fraction of the grinding slurry after pickling, and the mass ratio of the silicon powder, the grinding aid and the zirconia ball after pickling is 85: 15: and 300, carrying out wet grinding nanocrystallization treatment on the pickled silicon powder by using a pin-type nanometer sand mill, and separating zirconia balls after grinding to obtain nanometer silica sol slurry with the length dimension of 400-800 nm and the width and thickness dimensions of 50-100 nm.
Weighing the mixture with carbon content of more than 99.95 percent and average grain diameter D50 of 3.5 mu m1000g of natural graphite and 170g of furan resin are added into ethanol solution, the rotating speed is 510r/min, the frequency is 18kHz, and the power density is 0.41w/cm2After ultrasonic pre-dispersion for 42min, adding 433g of nano silica sol slurry, and carrying out ultrasonic mixing and dispersion for 56min at the same rotating speed, frequency and power density to obtain mixed slurry with the solid content of 23%.
And fifthly, carrying out spray granulation on the mixed slurry at the inlet temperature of 230 ℃ and the outlet temperature of 90 ℃ to obtain a secondary particle precursor with the average particle size D50 of 12 microns.
Sixthly, putting the secondary particle precursor into a high-temperature reaction kettle, wherein the flow of helium gas is 0.4m3Heating the mixture from room temperature to 420 ℃ at a heating rate of 3 ℃/min under the condition of 18r/min for 90min, and spraying the water-soluble phenolic resin solution to the surface of the secondary particle precursor in the reaction kettle by using a centrifugal spraying electric atomizer at room temperature according to the mass of the solid content of the water-soluble phenolic resin solution being 22% of that of the secondary particle precursor, wherein the rotating speed of the atomizer is 12000 r/min; and after the heat preservation is finished, heating to 810 ℃ at the temperature rise speed of 3 ℃/min according to the stirring speed of 35r/min, preserving the heat for 100min, naturally cooling to room temperature in the high-temperature reaction kettle, and stirring to obtain the silicon-carbon composite anode material precursor.
Seventhly, placing the silicon-carbon composite anode material precursor in a high-temperature atmosphere furnace, wherein the flow of krypton is 0.6m3Heating to 950 ℃ at the heating rate of 3 ℃/min in the atmosphere of/h, calcining for 2.5h, naturally cooling to room temperature in the furnace after the calcination is finished, scattering and grading to obtain the silicon-carbon composite negative electrode material for the lithium ion battery.
The silicon-carbon composite negative electrode material for the lithium ion battery obtained in the embodiment 2 is sieved by a 200-mesh sieve, and then physical performance and chemical performance tests are carried out. The average particle diameter D50 of the negative electrode material was 12.0. mu.m, and the specific surface area was 1.56m2The tap density of the negative electrode material powder is 1.17g/cm3The first discharge capacity at 0.1C is 535.0mAh/g, the first efficiency is 91.7%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is not less than 85.5%, and the test results are summarized in Table 1.
Example 3
Firstly, crushing the silicon mud into silicon powder with the particle size of less than 2 microns by a mechanical crusher.
Secondly, adding the silicon powder into 1.5mol/L sulfuric acid solution, wherein the adding amount is 45% of the mass of the acid solution, stirring and soaking for 3.0 hours at the rotating speed of 300r/min, and after acid washing is finished, performing suction filtration, centrifugal dehydration and drying to obtain the acid-washed silicon powder with the water mass content of less than 0.2%.
The flow rate of the neon gas is 0.6m3Under the protection of a/h atmosphere, propanol is used as a solvent, fatty alcohol-polyoxyethylene ether is used as a grinding aid, a mixed solution of acid-washed silicon powder, the grinding aid and the solvent is used as grinding slurry, a zirconia ball with the thickness of 0.08mm is used as a grinding medium, the acid-washed silicon powder accounts for 35% of the mass fraction of the grinding slurry, and the mass ratio of the acid-washed silicon powder to the grinding aid to the zirconia ball is 90: 10: and 300, carrying out wet grinding nanocrystallization treatment on the pickled silicon powder by using a pin-type nanometer sand mill, and separating zirconia balls after grinding to obtain nanometer silica sol slurry with the length dimension of 400-800 nm and the width and thickness dimensions of 50-100 nm.
Weighing 1000g of graphitized petroleum coke with the carbon content of more than 99.95 percent and the average particle size D50 of 5 mu m and 170g of phenolic resin, adding the weighed petroleum coke and the phenolic resin into a propanol solution, and controlling the rotating speed at 420r/min, the frequency at 16kHz and the power density at 0.37w/cm2After ultrasonic pre-dispersion for 54min, adding 285g of nano silica sol slurry, and carrying out ultrasonic mixing and dispersion for 72min at the same rotating speed, frequency and power density to obtain mixed slurry with the solid content of 26%.
And fifthly, carrying out spray granulation on the mixed slurry at the inlet temperature of 210 ℃ and the outlet temperature of 80 ℃ to obtain a secondary particle precursor, wherein the average particle size D50 is 14 microns.
Sixthly, putting the secondary particle precursor into a high-temperature reaction kettle, wherein the flow of neon is 0.6m3Heating the mixture from room temperature to 390 ℃ at a heating rate of 4 ℃/min under the condition of 21r/min stirring speed, preserving heat for 120min, spraying polyethylene glycol ether to the surface of a secondary particle precursor in a reaction kettle by utilizing a centrifugal spraying electric atomizer at room temperature according to the mass of the solid content of the polyethylene glycol ether being 18% of that of the secondary particle precursor, wherein the rotating speed of the atomizer is 14000 r/min; after the heat preservation is finished, the temperature is raised by 4 ℃/min according to the stirring speed of 40r/minAnd (3) heating to 770 ℃, keeping the temperature for 150min, naturally cooling to room temperature in the high-temperature reaction kettle, and stirring to obtain the silicon-carbon composite anode material precursor.
Seventhly, placing the silicon-carbon composite anode material precursor in a high-temperature atmosphere furnace, wherein the flow of argon is 0.8m3Heating to 1000 ℃ at the heating rate of 4 ℃/min in the atmosphere of/h, calcining for 2.0h, naturally cooling to room temperature in the furnace after the calcination is finished, scattering and grading to obtain the silicon-carbon composite negative electrode material for the lithium ion battery.
The silicon-carbon composite negative electrode material for the lithium ion battery obtained in the embodiment 3 is sieved by a 200-mesh sieve, and then physical performance and chemical performance tests are carried out. The average particle diameter D50 of the negative electrode material was 13.6. mu.m, and the specific surface area was 1.43m2The tap density of the negative electrode material powder is 1.18g/cm3The first discharge capacity at 0.1C is 484.8mAh/g, the first efficiency is 92.0%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is more than or equal to 88.3%, and the test results are summarized in Table 1.
As shown in FIG. 1, the XRD diffraction pattern of the negative electrode material of example 3, by comparing with the diffraction peaks of the corresponding standard PDF card, the strong diffraction peaks observed around 26.4 °, 44.4 °, 54.5 °, and 77.2 ° correspond to the (002), (101), (004), and (110) crystal planes of graphite (PDF card number: 41-1487), respectively; the strong diffraction peaks observed near 42.4 ° and 77.4 ° correspond to the (110) and (100) crystal planes of Si (PDF card number: 47-1186), respectively; the other stronger diffraction peaks correspond to carbon materials (PDF card number: 75-2078), respectively. The main components of the anode material can be found by the analysis of an XRD (X-ray diffraction) pattern, namely graphite, Si and amorphous carbon.
As shown in FIG. 2, the SEM image of the silicon powder after acid pickling of example 3 shows that the silicon powder particles are in the shape of long thin sheets with a length dimension of 800-1500 nm and a width and thickness dimension of 50-100 nm.
As shown in fig. 3, the negative electrode material obtained in example 3 has a sphere-like shape, uniform particle distribution, no nano silicon powder exposed outside, and smooth and flat particle surface, which indicates that the coating layer is completely, uniformly and densely.
Example 4
Firstly, the silicon mud is crushed into silicon powder with the particle size of less than 2 mu m by an ultrafine crusher.
Secondly, adding the silicon powder into 2.0mol/L phosphoric acid solution, wherein the adding amount is 55% of the mass of the acid solution, stirring and soaking for 2.5 hours at the rotating speed of 350r/min, and after acid washing, performing suction filtration, centrifugal dehydration and drying to obtain the acid-washed silicon powder with the water mass content of less than 0.2%.
Flow of argon gas is 0.6m3Under the protection of a/h atmosphere, isopropanol is used as a solvent, alkylphenol ethoxylates is used as a grinding aid, a mixed solution of acid-washed silicon powder, the grinding aid and the solvent is used as grinding slurry, a zirconia ball with the thickness of 0.08mm is used as a grinding medium, the acid-washed silicon powder accounts for 35% of the mass fraction of the grinding slurry, and the mass ratio of the acid-washed silicon powder to the grinding aid to the zirconia ball is 90: 10: and 300, carrying out wet grinding nanocrystallization treatment on the silicon powder subjected to acid pickling by using a high-energy nano ball mill, and separating zirconia balls after grinding to obtain nano silica sol slurry with the nano silicon length dimension of 400-800 nm and the width and thickness dimensions of 50-100 nm.
Fourthly, weighing 1000g of graphitized asphalt coke with the carbon content of more than 99.95 percent and the average grain diameter D50 of 6.5 mu m and 170g of polyvinyl alcohol, adding the weighed materials into the isopropanol solution, rotating at the speed of 330r/min, the frequency of 14kHz and the power density of 0.33w/cm2After ultrasonic pre-dispersion for 66min, adding 257g of nano silica sol slurry, and ultrasonically mixing and dispersing for 88min at the same rotating speed, frequency and power density to obtain mixed slurry with the solid content of 29%.
And fifthly, carrying out spray granulation on the mixed slurry at the inlet temperature of 190 ℃ and the outlet temperature of 80 ℃ to obtain a secondary particle precursor with the average particle size D50 of 14 microns.
Sixthly, putting the secondary particle precursor into a high-temperature reaction kettle with the argon flow of 0.6m3Heating the mixture from room temperature to 360 ℃ at a heating rate of 4 ℃/min under the condition of 24r/min for 120min, and spraying the water-soluble phenolic resin solution to the surface of the secondary particle precursor in the reaction kettle by using a centrifugal spraying electric atomizer at room temperature according to the mass of the solid content of the water-soluble phenolic resin solution being 16% of that of the secondary particle precursor, wherein the rotating speed of the atomizer is 14000 r/min; after the heat preservation is finished, stirring the mixture at the stirring speed of 40r/min to 4And (3) raising the temperature to 730 ℃ at a temperature rise speed of/min, preserving the temperature for 150min, naturally cooling the mixture to room temperature in the high-temperature reaction kettle, and stirring to obtain the silicon-carbon composite anode material precursor.
Seventhly, placing the silicon-carbon composite anode material precursor in a high-temperature atmosphere furnace, wherein the flow of neon is 0.8m3Heating to 1000 ℃ at the heating rate of 4 ℃/min in the atmosphere of/h, calcining for 1.5h, naturally cooling to room temperature in the furnace after the calcination is finished, scattering and grading to obtain the silicon-carbon composite negative electrode material for the lithium ion battery.
The silicon-carbon composite negative electrode material for the lithium ion battery obtained in example 4 is sieved by a 200-mesh sieve, and then physical properties and chemical properties are tested. The average particle diameter D50 of the negative electrode material was 15.5. mu.m, and the specific surface area was 1.50m2The tap density of the negative electrode material powder is 1.13g/cm3The first discharge capacity at 0.1C is 472.0mAh/g, the first efficiency is 92.2%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is more than or equal to 89.3%, and the test results are summarized in Table 1.
Example 5
Firstly, grinding the silicon mud into silicon powder with the particle size of less than 2 microns by a ball mill grinder.
Secondly, adding the silicon powder into 2.5mol/L carbonic acid solution, wherein the adding amount is 65% of the mass of the acid solution, stirring and soaking for 2.0 hours at the rotating speed of 400r/min, and after the acid cleaning is finished, performing suction filtration, centrifugal dehydration and drying to obtain the acid cleaned silicon powder with the water mass content of less than 0.2%.
The flow rate of the krypton gas is 0.8m3Under the protection of a/h atmosphere, n-hexane is used as a solvent, polyoxyethylene alkylamide is used as a grinding aid, a mixed solution of silicon powder, the grinding aid and the solvent after pickling is used as grinding slurry, a zirconia ball with the thickness of 0.1mm is used as a grinding medium, the silicon powder after pickling accounts for 40% of the mass fraction of the grinding slurry, and the mass ratio of the silicon powder, the grinding aid and the zirconia ball after pickling is 95: 5: and 300, carrying out wet grinding nanocrystallization treatment on the silicon powder subjected to acid pickling by using a high-energy nano ball mill, and separating zirconia balls after grinding to obtain nano silica sol slurry with the nano silicon length dimension of 400-800 nm and the width and thickness dimensions of 50-100 nm.
Fourthly, the graphitized product with the carbon content of more than 99.95 percent and the average grain diameter D50 of 8 mu m is weighedAdding 1000g of needle coke and 80g of polyacrylonitrile into tetrahydrofuran solution, wherein the rotating speed is 240r/min, the frequency is 12kHz, and the power density is 0.29w/cm2After ultrasonic pre-dispersion for 78min, adding 150g of nano silica sol slurry, and carrying out ultrasonic mixing dispersion for 104min at the same rotating speed, frequency and power density to obtain mixed slurry with the solid content of 32%.
And fifthly, carrying out spray granulation on the mixed slurry at the inlet temperature of 170 ℃ and the outlet temperature of 70 ℃ to obtain a secondary particle precursor with the average particle size D50 of 16 microns.
Sixthly, putting the secondary particle precursor into a high-temperature reaction kettle, wherein the flow of krypton is 0.8m3In the atmosphere of/h, the stirring speed is 27r/min, the temperature is increased from room temperature to 330 ℃ at the temperature increase speed of 5 ℃/min, the temperature is maintained for 150min, the heat preservation is started, the diethyl phthalate is sprayed to the surface of the secondary particle precursor in the reaction kettle by utilizing a centrifugal spraying electric atomizer at room temperature according to the solid content mass of the diethyl phthalate being 12 percent of that of the secondary particle precursor, and the rotating speed of the atomizer is 16000 r/min; and after the heat preservation is finished, heating to 690 ℃ at the temperature rise speed of 5 ℃/min according to the stirring speed of 45r/min, preserving the heat for 200min, naturally cooling to room temperature in the high-temperature reaction kettle, and stirring to obtain the silicon-carbon composite anode material precursor.
Seventhly, placing the silicon-carbon composite anode material precursor in a high-temperature atmosphere furnace, wherein the flow of helium gas is 1.0m3Heating to 1050 ℃ at the heating rate of 5 ℃/min in the atmosphere of/h, calcining for 1.0h, naturally cooling to room temperature in the furnace after the calcining is finished, scattering and grading to obtain the silicon-carbon composite negative electrode material for the lithium ion battery.
The silicon-carbon composite negative electrode material for the lithium ion battery obtained in example 5 is sieved by a 200-mesh sieve, and then physical properties and chemical properties are tested. The average particle diameter D50 of the negative electrode material was 17.5. mu.m, and the specific surface area was 1.23m2The tap density of the negative electrode material powder is 1.10g/cm3The first discharge capacity at 0.1C is 411.2mAh/g, the first efficiency is 92.0%, the cycle capacity retention rate at 100 cycles of 1C charge and discharge is more than or equal to 90.8%, and the test results are summarized in Table 1.
Example 6
Firstly, crushing the silicon mud into silicon powder with the particle size of less than 2 microns by using a jet mill.
Secondly, adding the silicon powder into a mixed solution of 3.0mol/L of equivalent acetic acid and oxalic acid, wherein the adding amount is 70% of the mass of the acid solution, stirring and soaking for 0.5h at the rotating speed of 500r/min, and after the acid washing is finished, performing suction filtration, centrifugal dehydration and drying to obtain the acid-washed silicon powder with the water mass content of less than 0.2%.
Flow rate of xenon gas is 1.0m3Under the protection of a/h atmosphere, taking N-methyl pyrrolidone as a solvent, taking fatty acid polyoxyethylene ester and polyoxyethylene alkyl ammonium as grinding aids, taking a mixed solution of silicon powder, the grinding aids and the solvent after acid washing as grinding slurry, taking a zirconia ball with the thickness of 0.1mm as a grinding medium, taking the silicon powder after acid washing to account for 45 mass percent of the grinding slurry, and taking the silicon powder, the grinding aids and the zirconia ball after acid washing to be 95: 5: and 300, carrying out wet grinding nanocrystallization treatment on the silicon powder subjected to acid pickling by using a high-energy nano ball mill, and separating zirconia balls after grinding to obtain nano silica sol slurry with the nano silicon length dimension of 400-800 nm and the width and thickness dimensions of 50-100 nm.
Weighing 1000g of graphitized mesophase carbon microspheres with the carbon content of more than 99.95 percent and the average particle size D50 of 10 mu m and 50g of styrene-butadiene rubber, adding the graphitized mesophase carbon microspheres and the styrene-butadiene rubber into an ethyl acetate aqueous solution, wherein the rotating speed is 150r/min, the frequency is 10kHz, and the power density is 0.25w/cm2And after 90min of ultrasonic pre-dispersion, 89g of nano silica sol slurry is added, and under the same rotating speed, frequency and power density, ultrasonic mixing and dispersion are carried out for 120min to obtain mixed slurry with the solid content of 35%.
And fifthly, carrying out spray granulation on the mixed slurry at the inlet temperature of 150 ℃ and the outlet temperature of 50 ℃ to obtain a secondary particle precursor with the average particle size D50 of 18 microns.
Sixthly, putting the secondary particle precursor into a high-temperature reaction kettle, wherein the flow of xenon is 1.0m3Stirring at 30r/min under the atmosphere of h, heating from room temperature to 300 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 180min, spraying the emulsified asphalt to the surface of the secondary particle precursor in the reaction kettle by using a centrifugal spraying electric atomizer at room temperature according to the solid content mass of the emulsified asphalt being 9% of the secondary particle precursor, wherein the rotating speed of the atomizer is 20000r/min, and the temperature is keptAnd after the temperature is finished, heating to 650 ℃ at the stirring speed of 60r/min and the temperature rise speed of 5 ℃/min, preserving the temperature for 240min, naturally cooling the high-temperature reaction kettle to room temperature, and finishing stirring to obtain the silicon-carbon composite anode material precursor.
Seventhly, placing the silicon-carbon composite anode material precursor in a high-temperature atmosphere furnace, wherein the nitrogen flow is 1.2m3Heating to 1100 ℃ at the heating rate of 5 ℃/min in the atmosphere of/h, calcining for 0.5h, naturally cooling to room temperature in the furnace after the calcination is finished, scattering and grading to obtain the silicon-carbon composite negative electrode material for the lithium ion battery.
The silicon-carbon composite negative electrode material for the lithium ion battery obtained in example 6 is sieved by a 200-mesh sieve, and then physical properties and chemical properties are tested. The average particle diameter D50 of the negative electrode material was 19.2 μm, and the specific surface area was 1.26m2The tap density of the negative electrode material powder is 1.09g/cm3The first discharge capacity at 0.1C is 370.0mAh/g, the first efficiency is 92.5%, the cycle capacity retention rate at 100 cycles of 1C charge-discharge is not less than 92.3%, and the test results are summarized in Table 1.
Comparative example
Firstly, adopting the commercial nano silicon powder.
Weighing 1000g of graphitized asphalt coke with the carbon content of more than 99.95 percent and the average particle size D50 of 6.5 mu m and 170g of polyvinyl alcohol, adding the weighed materials into an isopropanol solution, and rotating at a speed of 330r/min, a frequency of 14kHz and a power density of 0.33w/cm2After ultrasonic pre-dispersion for 66min, adding 90g of commercially available nano silicon powder with the average particle size D50 of 100nm, and ultrasonically mixing and dispersing for 88min under the same rotating speed, frequency and power density to obtain mixed slurry with 29% of solid content.
And thirdly, carrying out spray granulation on the mixed slurry at the inlet temperature of 190 ℃ and the outlet temperature of 80 ℃ to obtain a secondary particle precursor with the average particle size D50 of 14 microns.
Fourthly, placing the secondary particle precursor in a high-temperature atmosphere furnace with argon flow of 0.6m3Heating from room temperature to 360 ℃ at a heating rate of 4 ℃/min in an atmosphere of/h, preserving heat for 120min, heating to 730 ℃ at the heating rate of 4 ℃/min, preserving heat for 150min, and then carrying out self-heating cooling in the furnace to the room temperature to obtain secondary particles.
Fifthly, uniformly mixing the secondary particles and the coating agent phenolic resin in a mass ratio of 100:16 in a mixer, and then placing the mixture in a high-temperature atmosphere furnace with neon flow of 0.8m3Heating to 1000 ℃ at the heating rate of 4 ℃/min in the atmosphere of/h, calcining for 1.5h, naturally cooling to room temperature in the furnace after the calcination is finished, and scattering and grading to obtain the silicon-carbon composite negative electrode material.
And (3) screening the silicon-carbon composite negative electrode material obtained in the comparative example through a 200-mesh sieve, and then testing the physical property and the chemical property. The average particle diameter D50 was 18.5 μm, and the specific surface area was 3.85m2(iv) powder tap density of 0.92g/cm3The first discharge capacity at 0.1C is 450.2mAh/g, the first efficiency is 86.1%, the cycle capacity retention rate at 100 cycles of 1C charge-discharge is more than or equal to 75.2%, and the test results are summarized in Table 1.
The silicon source used in the invention is silicon mud which is a byproduct in silicon wafer production, has wide source and low price, and can effectively reduce the production cost of the cathode material. Meanwhile, the invention provides a new idea for energy-saving and environment-friendly treatment of the silicon wafer production by-product in the photovoltaic industry, and is beneficial to realizing high-value utilization of the silicon mud by-product. The silicon mud is waste materials generated when silicon wafers are processed through diamond wire-electrode cutting silicon ingots, silicon powder particles in the silicon mud are in a strip slice shape, the length dimension is 800-1500 nm, the width dimension and the thickness dimension are 50-100 nm, and the surface of the silicon mud is coated with a passivation film formed by organic polymers in diamond wire-electrode cutting liquid. According to the invention, the silicon mud is used as a silicon source, the nano silicon powder in the waste silicon powder is separated and purified to be used as a silicon raw material precursor, the source is wide, the price is low, and the production cost of the cathode material is favorably reduced. Silica powder exists in the silicon mud in a strip and flaky structure, and the nano silica powder obtained after the nanocrystallization treatment still keeps the original shape and structure, so that the lithium ions have stronger orientation in the embedding and embedding process of the lithium ions, and are in disordered distribution in secondary particles after being compounded and granulated with the micro-powder graphite, the concentrated release of stress generated by silicon volume expansion in the charge and discharge process of the negative electrode material in a single direction can be effectively relieved, and the cycle stability of the negative electrode material is effectively improved. The amorphous carbon intermediate layer formed by carbonizing the nonionic surfactant and the carbonizable binder in the secondary particles has good compatibility with the electrolyte, a compact solid electrolyte interface SEI film with a stable structure and good thermal stability can be formed on the interface, and the safety of the negative electrode material can be effectively improved.
The micro-powder graphite used in the invention is small-particle-size tailing in the production process of the lithium ion battery cathode, so that the utilization rate of the graphite raw material can be effectively improved, the production cost is reduced, and the pollution of tailing dust in the production of the lithium ion battery cathode material to the environment is reduced.
The cathode material has a core-shell structure with hard outside and soft inside, and is extremely suitable for high-rate charge and discharge. In the preparation process of the cathode material, the porosity and interface cavity defects are generated among the components of the secondary particles in a spray granulation mode, dynamic high-temperature fusion is combined, and after organic matters of the nonionic surfactant and the binder in the matrix of the secondary particles are softened and melted, the organic matters can be continuously infiltrated and permeated to the surfaces and contact interfaces of the nano silicon powder and the micro powder graphite in a liquid phase state to repair the internal cavities and the pore defects of the particles, so that the secondary particles have certain porosity and better particle compactness and structural stability. Along with the subsequent high-temperature calcination process, organic matters are decomposed to generate amorphous carbon to be coated on the surfaces of the nano silicon powder and the micro graphite, and the coated nano silicon powder and the coated micro graphite are bridged by chemical bonds, so that the particle compactness and the structural stability are effectively improved, and meanwhile, residual micro pores which are not completely repaired by high-temperature fusion in the secondary particles are randomly distributed in the amorphous carbon formed by carbonization and on the surfaces of the amorphous carbon formed by carbonization, so that a space can be reserved for the charge-discharge expansion of the nano silicon powder. The dynamic high-temperature fusion coating can ensure that the coating agent is uniformly and completely coated on the surfaces of the granulated particles, and a carbon coating layer with a uniform and compact structure is generated through high-temperature calcination, so that the mechanical strength of the negative electrode material can be effectively improved, the specific surface area is reduced, and the final negative electrode material has a core-shell structure with hard outside and soft inside and is suitable for high-rate charge and discharge.
The preparation method is simple, environment-friendly, easy to control process conditions, low in production cost and easy for industrial production.
Table 1 results of physical and chemical property tests of examples and comparative examples
Figure BDA0002392490610000241

Claims (7)

1. A preparation method of a silicon-carbon composite negative electrode material for a lithium ion battery comprises the following steps:
coarse powder of silicon mud
Crushing the silicon sludge to obtain silicon powder with the particle size of below 2 mu m;
the silicon mud is made of waste materials obtained after monocrystalline silicon or polycrystalline silicon is cut by diamond wires, the mass content of water is lower than 0.2%, and a passivation film formed by organic polymers in diamond wire cutting liquid is coated on the surface of the silicon mud;
second, acid cleaning
Stirring and soaking silicon powder in acid liquor with the concentration of 0.5-3 mol/L, wherein the mass of the silicon powder is 25-70% of that of the acid liquor, the stirring and soaking speed is 150-500 r/min, the stirring and soaking time is 0.5-5 h, after the stirring and soaking is finished, washing to be neutral, performing suction filtration, centrifugal dehydration and drying, and the mass content of water is lower than 0.2%, so as to obtain acid-washed silicon powder;
three, nano treatment
Taking a nonionic surfactant as a grinding aid, grinding and grinding the zirconium oxide balls with the diameter of 0.05-0.1 mm, and carrying out wet grinding nanocrystallization treatment on the acid-washed silicon powder in a protective gas atmosphere, wherein the mass ratio of the acid-washed silicon powder to the grinding aid to the zirconium oxide balls is 85-95: 15-5: 300, taking the acid-washed silicon powder, the mixed liquid of the grinding aid and the solvent as grinding slurry, wherein the acid-washed silicon powder accounts for 25-45% of the mass fraction of the grinding slurry, and separating zirconia balls after nano treatment to obtain nano silica sol slurry, wherein the length of the nano silica is 400-800 nm, and the width and thickness of the nano silica are 50-100 nm;
fourthly, ultrasonic dispersion
According to the mass ratio of the micro-powder graphite to the carbonizable binder of 100: 5.0 to 20.0, carrying out ultrasonic pre-dispersion on the micro-powder graphite and the carbonizable binder in a solvent at the rotating speed of 150 to 600r/min, the frequency of 10 to 20kHz and the power density of 0.25 to 0.45w/cm2After the ultrasonic pre-dispersion time is 30-90 min, adding the nano silica sol slurry, and performing ultrasonic mixing dispersion at the rotating speed of 150-600 r/min at a frequency ofThe ratio is 10-20 kHz, and the power density is 0.25-0.45 w/cm2And (3) performing ultrasonic mixing and dispersing for 40-120 min to obtain mixed slurry with the solid content of 20-35%, wherein the mass ratio of the nano silicon powder to the micro graphite powder is 4-15: 100, respectively;
spray granulation
Carrying out spray drying granulation on the mixed slurry, wherein the inlet temperature of the spray drying granulation is 150-250 ℃, and the outlet temperature of the spray drying granulation is 50-110 ℃, so as to obtain a secondary particle precursor with larger defects of holes and pores;
sixthly, high-temperature fusion and coating
Stirring the secondary particle precursor at a stirring speed of 15-30 r/min under a protective gas atmosphere, heating to 300-450 ℃ at a heating speed of 2-5 ℃/min, preserving heat for 60-180 min, starting heat preservation, atomizing the liquid coating agent at room temperature according to the mass of the solid content of the liquid coating agent being 9-25% of that of the secondary particle precursor, and spraying the atomized liquid coating agent onto the surface of the secondary particle precursor in a reaction kettle; after the heat preservation is finished, heating to 650-850 ℃ in a second heat preservation area at a stirring speed of 25-60 r/min and a temperature rise speed of 2-5 ℃/min, preserving the heat for 60-240 min, naturally cooling to room temperature, and stirring to obtain a silicon-carbon composite anode material precursor; the first heating, heat preservation and stirring are carried out for fusion, so that the nonionic surfactant and the carbonizable binder in the secondary particle precursor substrate can be fully softened and melted, and the defects of cavities and pores are continuously infiltrated and repaired in a liquid phase state;
seven, high temperature calcination
Heating the precursor of the silicon-carbon composite negative electrode material to the calcining temperature of 900-1100 ℃ at the heating rate of 3-5 ℃/min under the protective gas atmosphere, calcining for 0.5-3.0 h, and naturally cooling to the room temperature after the calcining is finished to obtain the silicon-carbon composite negative electrode material for the lithium ion battery; and finally, carrying out high-temperature fusion on the secondary particles, wherein the non-ionic surfactant and the carbonizable binder in the secondary particle precursor substrate are subjected to heat treatment in a second heat preservation area and high-temperature calcination in the step seven to generate amorphous carbon, the amorphous carbon is uniformly coated on the surfaces of the nano silicon powder and the micro graphite, and the coated nano silicon powder and the coated micro graphite are bridged by chemical bonds, and meanwhile, the residual micro pores which are not completely repaired in the secondary particles through high-temperature fusion are randomly distributed in and on the surface of the amorphous carbon formed through carbonization.
2. The preparation method of the silicon-carbon composite anode material for the lithium ion battery according to claim 1, characterized by comprising the following steps: the second acid solution in the step is more than one of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, carbonic acid, acetic acid and oxalic acid solution.
3. The preparation method of the silicon-carbon composite anode material for the lithium ion battery according to claim 1, characterized by comprising the following steps: the nonionic surfactant in the third step is more than one of polyethylene glycol, polyvinylpyrrolidone, fatty alcohol-polyoxyethylene ether, alkylphenol ethoxylate, polyoxyethylene alkylamide, fatty acid polyoxyethylene ester and polyoxyethylene alkylammonium; the wet grinding slurry is prepared from more than one of ethanol, propanol, acetone, isopropanol, N-hexane and N-methylpyrrolidone as solvent, the protective gas is nitrogen, helium, neon, argon, krypton or xenon, and the flow rate is 0.2-1.0 m3/h。
4. The preparation method of the silicon-carbon composite anode material for the lithium ion battery according to claim 2, characterized by comprising the following steps: the graphite micropowder obtained in the fourth step is a small-particle-size tailing in the production process of the lithium ion battery negative electrode material, the average particle size D50 is 2-10 microns, the graphite micropowder comprises more than one of graphitized mesophase carbon microspheres, petroleum coke, pitch coke, needle coke and natural graphite, the carbon content is more than 99.95%, and the carbonizable binder is more than one of modified alkyd resin, furan resin, phenolic resin, polyvinyl alcohol, polyacrylonitrile and styrene butadiene rubber; the solvent is more than one of deionized water, methanol, ethanol, propanol, isopropanol, tetrahydrofuran and ethyl acetate.
5. The preparation method of the silicon-carbon composite anode material for the lithium ion battery according to claim 1, characterized by comprising the following steps: the liquid coating agent in the sixth step is one of emulsified asphalt, water-soluble phenolic resin solution, polyglycol ether and diethyl phthalateThe above; the atomization rotating speed is 8000-20000 r/min; the protective gas is nitrogen, helium, neon, argon, krypton or xenon, and the flow rate is 0.2-1.0 m3/h。
6. The preparation method of the silicon-carbon composite anode material for the lithium ion battery according to claim 1, characterized by comprising the following steps: the protective gas in the step seven is nitrogen, helium, neon, argon, krypton or xenon, and the flow rate is 0.4-1.2 m3/h。
7. The silicon-carbon composite negative electrode material for the lithium ion battery, which is prepared by the preparation method of the silicon-carbon composite negative electrode material for the lithium ion battery according to any one of claims 1 to 6, is of a core-shell structure, the core contains nano silicon powder and micro graphite, the nano silicon powder is in a strip sheet shape, the core is formed by strip sheet nano silicon powder and micro graphite, amorphous carbon coated on the surfaces of the nano silicon powder and the micro graphite, and amorphous carbon bridged around the coated nano silicon powder and micro graphite, micro pores are distributed in the amorphous carbon and on the surface of the amorphous carbon, the amorphous carbon is formed by high-temperature carbonization of a non-ionic surfactant and a carbonizable binder at 650-1100 ℃, and the mass ratio of the nano silicon powder, the micro graphite, the non-ionic surfactant and the carbonizable binder is 4-15: 100: 5.0 to 20.0; the shell is a carbon coating layer coated on the surface of the core, and the mass of the coating layer is 5-15% of that of the core;
the nano silicon powder and the micro powder graphite are randomly and uniformly distributed;
the length dimension of the nano silicon powder is 400-800 nm, and the width and thickness dimensions are 50-100 nm; the average particle size D50 of the micro powder graphite is 2-10 μm;
the nano silicon powder is made of waste materials obtained after monocrystalline silicon or polycrystalline silicon is cut by diamond wires, and the surface of the nano silicon powder is coated with a passivation film formed by organic polymers in diamond wire cutting liquid.
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